textile

Topics: Water pollution, Sewage treatment, Textile manufacturing Pages: 14 (1507 words) Published: October 12, 2013
3
Textile Organic Dyes –
Characteristics, Polluting Effects and
Separation/Elimination Procedures from
Industrial Effluents – A Critical Overview
Zaharia Carmen and Suteu Daniela
‘Gheorghe Asachi’ Technical University of Iasi,
Faculty of Chemical Engineering and Environmental Protection, Romania
1. Introduction
The residual dyes from different sources (e.g., textile industries, paper and pulp industries, dye and dye intermediates industries, pharmaceutical industries, tannery, and Kraft bleaching industries, etc.) are considered a wide variety of organic pollutants introduced into the natural water resources or wastewater treatment systems. One of the main sources with severe pollution problems worldwide is the textile industry and its dye-containing wastewaters (i.e. 10,000 different textile dyes with an estimated annual production of 7.105 metric tonnes are commercially available worldwide; 30% of these dyes are used in excess of 1,000 tonnes per annum, and 90% of the textile products are used at the level of 100 tonnes per annum or less) (Baban et al., 2010; Robinson et al., 2001; Soloman et al., 2009). 10-25% of textile dyes are lost during the dyeing process, and 2-20% are directly discharged as aqueous effluents in different environmental components. In particular, the discharge of dye-containing effluents into the water environment is undesirable, not only because of their colour, but also because many of dyes released and their breakdown products are toxic, carcinogenic or mutagenic to life forms mainly because of carcinogens, such as benzidine, naphthalene and other aromatic compounds (Suteu et al., 2009; Zaharia et al., 2009). Without adequate treatment these dyes can remain in the environment for a long period of time. For instance, the half-life of hydrolysed Reactive Blue 19 is about 46 years at pH 7 and 25°C (Hao et al., 2000).

In addition to the aforementioned problems, the textile industry consumes large amounts of potable and industrial water (Tables 1, 2 and Fig. 1) as processing water (90-94%) and a relatively low percentage as cooling water (6-10%) (in comparison with the chemical industry where only 20% is used as process water and the rest for cooling). The recycling of treated wastewater has been recommended due to the high levels of contamination in dyeing and finishing processes (i.e. dyes and their breakdown products, pigments, dye intermediates, auxiliary chemicals and heavy metals, etc.) (Tables 3, 4 and 5) (adapted from Bertea A. and Bertea A.P., 2008; Bisschops and Spanjers, 2003; Correia et al., 1994; Orhon et al., 2001).

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Organic Pollutants Ten Years After
the Stockholm Convention – Environmental and Analytical Update

56
Type of finishing process
Raw wool washing
Wool finishing
Fabric finishing

Short process

Complex processing
Cloth finishing

Simplified processing

Complex process

Panty processing
Carpet finishing
Fibre finishing
Non-fabrics finishing
Yarn finishing

Water consumption, 10-3 m3 /kg textile product
Minimum
Medium
Maximum
4.2
11.7
77.6
110.9
283.6
657.2
12.5
10.8

78.4
86.7

275.2
276.9

8.3
20
5.8

135.9
83.4
69.2

392.8
377.8
289.4

8.3
3.3
2.5
33.4

46.7
100.1
40
212.7

162.6
557.1
82.6
930.7

Table 1. Specific water consumption in textile finishing processes (adapted from Bertea A. & Bertea A.P., 2008)

Fig. 1. Specific water consumption in different operations of textile finishing (EPA, 1997) Operation/Process

General facilities
Preparation
Dyeing
Printing
Wetting
Fabrics washing
Finishing

Water consumption (% from total
consumption of the textile plant)
Minimum Medium Maximum
6
14
33
16
36
54
4
29
53
42
55
38
0.3
0.4
0.6
3
28
52
0.3
2
4

Organic load (% from total
organic load of the textile plant)
Minimum Medium Maximum
0.1
2
8
45
61
77
4
23
47
42
59
75
0
0.1
0.1
1
13
25
0.1
3
7

Table 2. Water...
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